Answer: It may be that the soil is too dry. This plant does best in soil that is evenly moist yet well drained meaning damp like a wrung out sponge, never soaking wet and never bone dry. The soil should have lots or organic matter or humus in it so it can hold moisture (and air.) To help keep the soil damp it should be mulched with several inches of organic mulch in a flat layer over the roots.
It may be that it is in too much sun; partial shade for this plant means bright dappled light all day or morning-only sun. If it is in aftrnoon sun then the location would be too hot for it.
I hope this helps you trouble shoot.
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